A Jumping Spider’s Pounce Relies on Blurry Vision

Blurry vision in humans often results in a prescription for glasses, contacts, or even surgery to restore a person’s vision to 20/20. For jumping spiders, however, blurry vision is an asset. Research by a team of scientists at Osaka City University in Japan indicates that the key to a jumping spiders leaping prowess is its unusual method of depth perception. The research, led by Akihisa Terakita, Mitsumasa Koyangi, and Takashi Nagata, utilized a variety of techniques to study the connection between jumping spiders vision and leaping acuity, including molecular biology and electrophysiology.

Humans and some other animals use binocular stereoscopic vision to perceive depth. Other species utilize far less sophisticated methods to perceive changes in depth. For example, most insects use motion parallax, or the movement of their heads in a side-to-side motion, to determine changes in depth. Blurry vision, or image defocus, does have a place in depth perception, however. Research has shown that humans use image defocus as a way to roughly estimate the relative depth of objects. Interestingly, jumping spiders use image defocus as an absolute measure of depth.

Jumping spiders use their two pairs of larger forward-facing eyes and smaller anterior lateral eyes to approach and successfully pounce on potential prey. By covering up the spiders anterior lateral eyes, the researchers found that the spiders principal forward-facing eyes were most important for depth perception. Through their studies, the scientists discovered that a jumping spiders retina is made up of four layers. The first two layers are most sensitive to green light, while the second and third layers are most sensitive to ultraviolet (UV) light. Green light that enters the retina is only clearly focused on the first layer. The second layer only receives a blurry, defocused image. The amount of defocus is proportional to the distance of the object to the lens. In other words, the larger the amount of defocus, the farther away the object is. Conversely, the smaller the amount of defocus, the closer the object is to the spider. This use of defocus to perceive depth makes a jumping spiders vision unlike any other animal.

The researchers tested their hypothesis by observing the spiders ability to jump under a variety of different lighting conditions. When exposed to red light, the spiders jumped short of their prey. This is because the retinal images were less-fuzzy under red light, which made the spiders think their prey was closer than it really was. However, under green light, the spiders nearly always successfully pounced on their prey.

According to the researchers, the spiders principal eyes are a real-life example of depth from defocus, a notable depth measurement technique that is being developed for computer vision. The scientists think that gaining an understanding of how jumping spiders see may inform the development of this form of vision in computers and also have implications for the development of related technologies as well.

Results from the scientists’ research were published in the January 27, 2012 issue of the journal Science. Scientists who contributed to this research included Takashi Nagata, Mitsumasa Koyanagi, Hisao Tsukamoto, Shinjiro Saeki, Kunio Isono, Yoshinori Shichida, Fumio Tokunaga, Michiyo Kinoshita, Kentaro Arikawa, and Akihisa Terakita.

The alteration of there sight when different colors (red,green) are surrounding revolves around the color of the plants and the color of themselves, (them seeming to be red) if you are jumping at you victim it would me logical if your eyes are tuned to perverse better around green light when the item you are jumping from is in fact green the majority of the time. The only flaw in this is with the decrease in perception when they are surrounded by red light. Would it be used to deter group hunting this possible, but it is also counter productive then the item you are jumping form is also red. But as there are a low number of red colored items in nature except in the season of fall. If my hypothesis about there eyes correlating with colors in there environment were to be fact, then i would assume that their environment would have short falls or none, or plants that do not change color in the fall/whiner, or something completely different form what i have spoken of!